Here's another reason why you shouldn't marry your cousin

A significant percentage of people worldwide are born to parents who are first- or second-cousins, largely in Asia and eastern Africa.

First cousins who marry run twice the risk of having a child with genetic abnormalities, according to a previous Health24 article.

Now a new study suggests that children born to parents who are cousins have a significant risk for developing a mood disorder – such as depression or anxiety.

Risk of mood disorder

For adults whose parents are first-cousins, the risk is triple that of people whose parents are unrelated, the researchers reported. And, mood disorder risk is also significantly higher among children of second-cousins, they said.

"The size of this association is significant, and understanding why children of 'related parents' are at an increased risk of psychoses and common mood disorders warrants further research," said study lead author Aideen Maguire. She is a lecturer with the Center for Public Health at Queen's University Belfast in Northern Ireland.

The findings – based on an analysis of nearly 364 000 people born in Northern Ireland between 1971 and 1986 – may seem unremarkable at first glance. But 10% of people worldwide are born to parents who are first- or second-cousins, largely in Asia and eastern Africa.

Practice banned in three nations

Fewer than 1% of Western marriages fall into this category of what is known as "consanguineous marriage". Though marriage between blood relatives increases the risk of genetic defects in offspring, the practice is banned in only 3 nations: the United States, North Korea and China.

The study findings were published online in JAMA Psychiatry.

Of the men and women included in the current study, 609 – or 0.2% – had been born to parents who were first- or second-cousins. Of those, 349 were born to second-cousin parents, and 260 were resulted from first-cousin pairings.

Need for counselling

The researchers inferred adult mental illness when any offspring had been prescribed an antidepressant, anti-anxiety or anti-psychotic medication at least once between 2010 and 2014.

As many as 36% of adults who had been born to first-cousin couples had been prescribed either an antidepressant or anti-anxiety drug. This compared with about 31% of second-cousin offspring, and about 27% of those born to unrelated parents, the findings showed.

Almost 9% of first-cousin offspring had been given antipsychotic meds, compared with roughly 4% of second-cousin offspring, and about 3% of unrelated offspring, the study authors said.

Based on those findings, Maguire suggested that couples should be counselled about the reproductive risks associated with consanguineous unions.

However, not all geneticists agree with the above findings, and according to Dr Arno Motulsky, a professor emeritus of medicine and genome sciences at the University of Washington, and the senior author of report published in The Journal of Genetic Counseling, there is only a slightly increased risk for genetic defects in children of first cousins, which in terms of general risks in life is not very high.

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The information on Health24 is for educational purposes only, and is not intended as medical advice, diagnosis or treatment. If you are experiencing symptoms or need health advice, please consult a healthcare professional. See additional information.